This application claims the priority of Korean Patent Application No. 2004-65881, filed on Aug. 20, 2004, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a radial-flow turbine wheel, and more particularly, to a radial-flow turbine wheel capable of restraining creation and propagation of a crack due to thermal stress, as well as improving a turbine efficiency.
2. Description of the Related Art
In general, a gas turbine is powered by expansion of an operating fluid of high temperature and high pressure, which is generated from the combustion process of a combustor, to drive a compressor coupled coaxially to the gas turbine. In an internal combustion engine with a turbocharger, a high-pressure gas compressed by the compressor is supplied to a fuel cell or a combustion cylinder of the internal combustion engine.
FIG. 1 is a cross-sectional view of a common turbocharger driven by such a gas turbine. Referring to FIG. 1, during operation of an internal combustion engine (not shown) coupled to the turbocharger, an exhaust gas F firstly flows in a spiral inflow casing 6 of the turbine. The exhaust gas F is accelerated in the inflow casing 6, and flows to turbine wheel 30. The exhaust gas F is expanded in the turbine wheel section 30, thereby generating an output to drive rotary shaft 5 and compressor wheel 4. The compressor wheel 4 compresses air A and supplies the compressed air to a combustion cylinder (not shown). Reference numeral C indicates the center of the rotary shaft 5.
FIG. 2 shows a conventional radial-flow turbine wheel 30 including a hub 10 and a plurality of turbine blades 20 formed around the hub 10 at constant intervals. The exhaust gas F flowing into the turbine wheel 30 flows along the turbine blades 20. In this process, the turbine blades 20 are urged to move in a rotating direction by the flow of exhaust gas F, so as to rotate the turbine wheel 30. According to the prior art, in order to reduce thermal stress and the weight of the gas turbine, a desired portion between the turbine blades 20 is cut away to form a scallop 60. As, a result, an outermost rear periphery 10a of the hub between the adjacent turbine blades has an inwardly concave shape.
However, an excessive formation of such scallops 60 results in deterioration of turbine efficiency. In particular, referring to FIG. 3, when the scallops are excessively formed (i.e., an outer radius R2 of the periphery 10a is remarkably reduced relative to the outer radius R1 of the turbine blade 20), the exhaust gas flowing into the turbine wheel 30 via a flow path may collide against the periphery 10a (indicated by F1) or may be leaked toward a back area B through a gap between the turbine wheel 30 and a wall 15 (indicated by F2). Since the exhaust gas colliding against the periphery 10a or leaked toward a back area B does not function as energy to drive the turbine wheel 30, there is a driving loss, which deteriorates turbine efficiency.